This invention relates to the manufacture of fibrous webs, and especially to apparatus for depositing dry fibers from an air suspension thereof onto a moving forming wire to form a fibrous web, such as paper.
Apparatus for depositing dry fibers generally takes the form of a distributor housing having a screen over an outlet opening facing a forming wire, and an inlet opening for directing a suspension of fibers in air from a suitable source into the housing for flow through the screen onto the wire. Rotary impeller means provided in the housing is operative to distribute the fibers over the screen to achieve uniform deposition of fibers on the forming wire.
Apparatus comprising multiple impellers rotatable about vertical axes and disposed in side-by-side relation above a planar screen extending over the forming wire are found in the art, but have a disadvantage in that spaces between the impellers contribute to variations in flow of the fibers through the screen, thereby detracting from uniformity of web formation in its cross machine direction.
Impellers rotatable about horizontal axes parallel to the plane of the forming wire, and extending transversely of the direction of wire movement, have been used in combination with a cylindrically shaped screen to improve web formation in its cross machine direction. Difficulties are still encountered, however, since the impeller blades extend parallel to their rotational axes, and there is often random motion of fibers in the housing in a cross machine direction tending to detract from uniformity of web formation.
U.S. Patents exemplary of the hereinabove described prior art are identified and briefly described in what follows:
U.S. Pat. No. 2,931,076 discloses apparatus for forming webs by dry-laying fibers from a dispensing chamber 15 through a foraminous, semi-cylindrical separating wall 16 onto a foraminous collecting wall 21, a series of disintegrating blades 18 being mounted for rotation about the axes of wall 16, transversely of the direction of movement of collecting wall 21; U.S. Pat. No. 3,644,078 discloses apparatus for dry-forming webs including multiple rotational elements 80, 81 above a screen 75 wherein the elements are in parallel array extending transversely of the direction of movement of forming wire 85;
U.S. Pat. No. 4,335,066 discloses impellers rotatable about vertical axes and in side-by-side relation to create a racetrack pattern of fibers caused to pass through a screen constructed to provide uniform distribution.
U.S. Pat. No. 4,264,289 discloses impellers similar to those of the '066 patent, and a screen construction for ensuring uniform fiber distribution; and
U.S. Pat. Nos. 4,169,699, 4,144,619, 3,984,898, and 3,645,457 disclose further examples of fiber distributors, each having a rotational element arranged to rotate about an axis parallel to a forming wire and extending transversely of the direction of movement of the wire.
None of the hereinabove described patents directed to horizontally rotational impellers suggests helical blading for the impellers.
It is a general objective of the invention to provide an improved distributor construction including helically bladed impellers for uniformly depositing dry-fibers on a forming wire in formation of a web of uniform thickness.
It is a further and specific objective of the invention to provide an improved dry-fiber distributor apparatus including a horizontal axis, rotational impeller having helical blades in novel cooperative disposition with respect to an impeller housing and a cylindrically-shaped screen extending over its outlet opening for achieving uniform fiber distribution on a forming wire.